linux-kernel - Re: [PATCH] arm64: dts: x1e80100-crd: describe HID supplies

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Message-ID: <Zxu2uedfWhAYSCrE@hovoldconsulting.com>
Date: Fri, 25 Oct 2024 17:18:17 +0200
From: Johan Hovold <johan@...nel.org>
To: Stephan Gerhold <stephan.gerhold@...aro.org>
Cc: Abel Vesa <abel.vesa@...aro.org>,
	Johan Hovold <johan+linaro@...nel.org>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konradybcio@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: x1e80100-crd: describe HID supplies

On Wed, Oct 16, 2024 at 06:43:26PM +0200, Stephan Gerhold wrote:
> On Tue, Oct 15, 2024 at 04:41:13PM +0300, Abel Vesa wrote:
> > On 24-10-15 14:24:27, Johan Hovold wrote:
 
> > > +&pm8550ve_8_gpios {
> > > +	misc_3p3_reg_en: misc-3p3-reg-en-state {
> > > +		pins = "gpio6";
> > > +		function = "normal";
> > > +		bias-disable;
> > 
> > Maybe output-enable and input-disable are needed. Can you please check?
> 
> FWIW, there is a reason behind explicitly describing the intended
> direction of the pin for PMIC GPIOs with properties like "output-enable"
> or "input-disable": On QC platforms, PMIC GPIOs can be either in "input"
> mode, "output" mode, or "input+output" mode. If you don't specify
> exactly what you want, then the pinctrl-spmi-gpio driver will only add
> to the existing configuration.
> 
> For the configuration above this means:
> 
>  1. If GPIO6 is disabled or in "output" mode during boot, the resulting
>     mode will be "output".
> 
>  2. If GPIO6 is in "input" mode during boot, the resulting mode will be
>     "input+output".
> 
> I don't know if "input+output" mode has any negative impact compared to
> pure "output" mode. We usually want to have the pins in a consistent
> state though (i.e. independent of the boot up state).

Fair enough. I was worried that configuring the pin as an output without
setting the output value could cause trouble (e.g. always default to
low), but it seems at least the Linux driver handles that.

Johan